1. Field of the Invention
This invention relates to stereo sound recording methods with sound pickup systems, i.e., positioned microphones, that find use in live personal and professional recording activities when coupled to any professional recorder or any of the numerous recording stereo deck/portable cassette tape players or sound recording equipment in consumer usage.
2. Description of Prior Art
It is well known that the natural acceptance of stereo sound playback/recording technology for consumer products, i.e., records, tapes, movies, etc. and consumer recording use has brought a multiplicity of recording microphones that permit the professional recording engineer as well as the amateur recording enthusiasts to capture live stereo sound. Moreover, the physical/mental way that we process the sound we hear has brought many different approaches to the design of said pickups/systems.
Since stereo involves information on two separate channels, more than one microphone is always used. Stereo, in its simplest form, consists of only left and right appearing sound direction, with the sound in between a mix of left and right amplitude signals. Hence, a perfect center-appearing sound can be fabricated by only mixing a left and right channel in equal amplitudes. This is precisely the technique used to produce many stereo sound recordings from monophonic sources (one microphone).
Stereo sound can also contain more complete signal information, as in the case of live field recordings, in the phase or timing arrival of sound at the pickups. This said signal information, combined with the amplitude information aforementioned, gives a more convincing illusion of the sound's left/right position and depth (as opposed to two-dimensional flat source reproduction) when played back on headphones and loudspeakers. In addition to the amplitude and timing components of stereo sound, it has been well known that additional sonic positional information is contained in the frequency response contour effect that the ears (external projecting ear features) and the inner ear canal features produce. These last features complete the realism of up/down/front/back/near/far when recorded.
Prior art has evolved to accommodate the complete stereo information gathering in this order: two microphones feed into two discrete channels of a recorder and, when said microphones are separated by a simple flat barrier, provide separate left and right information signals, but the results are without depth realism. The additional aspect of sound source depth is established by moving the microphones a specific minimum/maximum distance apart while maintaining the left/right barrier (approximately 7"-10"). The depth of the recording is further enhanced by replacing the two-dimensional barrier with a smooth three-dimensional projection in the general proportions of the human head or similar object. The two microphones are then positioned in the ear area of the improved three-dimensional barrier.
Prior art furthered the refinement of technique and equipment by not only simulating the general shape of the head but also by simulating the ear flaps and inner canal as well, positioning the microphones inside the dummy head.
The prior art then had to take a step back, for it was found that the signal now recorded in the dummy head/ear/canal passage was only convincing during headphone reproduction (not loudspeakers), with the best results from the person from which the dummy head/ears was directly modeled.
To overcome this "custom-tailored-for-only-one-person" recording limitation, the microphone position was moved to the entrance of the ear canal, referenced by Griese, et al in U.S. Pat. No. 3,969,583, at 10 mm distance from the opening. This provided recordings with better realism to more listeners removed from the subject model but only during headphone reproduction.
The merits associated with this aforementioned technique is called Binaural (two-ear) recording, which is not to be confused with the intentional proper playback environment, namely, headphones. These merits were offset by some drawbacks, however.
The prior art shows numerous dummy head type pickups as by Doi in U.S. Pat. No. 4,068,091 and personally-worn microphone devices for binaural recording, including those as in U.S. Pat. No. 3,969,583 hooked into the ear canal, those designed by Yasuda as in U.S. Pat. No. 4,010,335 inserted as a plug into the ear opening, and those also designed by Yasuda, as in U.S. Pat. No. 4,037,064 enclosed "earmuff" style windscreen assemblies. Those users who used these personally-worn devices as mentioned found them uncomfortable and often painful, as in the case of ear-inserted designs. Those amateur recording enthusiasts who endured the physical discomfort during live events also caused the unavoidable mental discomfort to those around the recordist--those who might only want to enjoy the simple activity of listening at a concert in a restful reposed position did not wish to be distracted by an obvious intrusion of microphones, especially in or on someone's ears as in the Usami, et al design as in U.S. Pat. No. 4,088,849 and such. This intrusion also limited candid recording especially with dummy head size pickups as with U.S. Pat. No. 4,068,091. Lastly, all of the prior art of the personally-worn binaural recording devices have one problem that is immediately obvious--namely, the impaired hearing of the wearer! Everything in, around the close vicinity/proximity of or covering the ears of a person changes the sound heard or distorts the signal arriving at the eardrums.
Therefore, those aforementioned recording users, when willing to endure the discomforts, must also compromise the high quality live listening experience for some future time at which said person must, solely or with few others, don headphones to hear the sonic recreation of the performance.
Thus, prior art has left this pursuit to the few die-hard recording buffs with numerous headphone sets/output equipment so that they don't completely die of loneliness with unshareable recordings.
Past attempts to frequency/phase adjust the output of such devices so that loudspeaker output/reproduction could recreate the real depth and tonal balance of the live sound as in U.S. Pat. No. 4,010,335 have largely failed to overcome the headphones-only limitation.
There is little wonder that the original recording enthusiasm generated by this said technique in the seventies has all but disappeared, only to be occasionally used for movie sound tracts, with the resulting effect of very few binaural recording pickups being manufactured and presently sold. This is ironic since the number of professional and consumer portable recorders has grown, making portable live recording more practical than ever before.
The handheld versions of stereo sound capturing pickups, while physically unimpairing while being held in clamping mounts or stands, remain obtrusive to the casual onlooker. They also produce largely unnaturally distorted and two-dimensional sounding recordings on headphones and loudspeakers alike. These microphones contain two or more pickup elements arranged such that two of the elements face directly left and right; the elements are usually of unidirectional design, though they can be of omni-directional design. These same handheld versions place the said pickup elements very close together within a common case, so that there is no way they can record the necessary acoustic delay associated with normal left and right hearing as done by the ears of a person. The recordings, accordingly, have a decided flat and two-dimensional character since none of these necessary depth perception sonic delayed signals are recorded.
In addition, these same microphones often use pickups of unidirectional design which cause a distortion and cancellation of off-axis sound sources. While these microphones give acceptable performance when very close to the intended sound source, placement of these microphones at a moderate distance from the sound stage magnifies the distortion to unacceptable levels. This distortion is further increased by clever one-piece stereo microphones which have three pickup elements. The third element is concerned with the reception of the center channel of the sound stage so that the output of said pickup can be subtracted from the left and right pickup outputs to enhance the stereo separation effect of the microphone. While this does increase the apparent separation response of these small assemblies, the resulting phase distortion from all of this synthesizing produces outputs ranging from inferior to awful.
Needless to say, user satisfaction and acceptance of these products is very low. Prospective buyers of microphone equipment for stereo recording who have done their homework in reviewing available equipment usually opt for two separate and quite obvious to view microphones to provide them with at least a low distortion recording. These said buyers then separate the individual microphones by some distance, usually one to eight feet, to capture some fraction of the live performance depth and field. This approach, again, is only for the professional and die-hard amateurs and not for the public in general with a more casual interest in live recording.